Oil mining is an old concept dating back thousands of years. In contrast to more commonly known surface techniques for recovering oil in which wells are drilled downwardly to the oil bearing formation and the oil is then pumped up the well bore to the surface, the simplest oil mining technique (i.e., gravity drainage) involves mining tunnels under the oil bearing formation and then drilling completion holes upwardly into the oil reservoir. The oil then drains downwardly by gravity where it is collected and eventually pumped to the surface.
The term "oil mining" actually encompasses a spectrum of processes designed to free petroleum from conventionally depleted fields and from fields not otherwise workable by conventional techniques. In addition to gravity drainage, two other basic oil mining methods include extractive and capillary interchange. In extractive mining, the oil bearing rock is removed and processed in underground or surface facilities. With this method, essentially all of the in-place petroleum is recovered. However, because of high costs, it is primarily only feasible for use in reservoirs with thick and rich petroleum seams and with little or no overburden and in host environments (e.g., unconsolidated sand) where minimal processing will easily remove the petroleum. In the capillary interchange or "flip-flop" method, petroleum is recovered from shallow deposits of heavy oil and tar sand by first removing the overburden or forming a cavern above the deposit. A containment is then constructed and the partially exposed oil or tar sand deposit is flooded with a hot, high-density, saline solution. The heat from the water reduces the viscosity of the oil and the difference in specific gravities of the saline solution and petroleum cause the two to exchange positions or flip-flop. The oil migrates upwardly and is recovered from the saline solution. With this method, laboratory tests indicate that recovery will actually be effective over an area greater than the exposed portion of the deposit. As compared to the extractive mining process, none of the oil bearing sand or rock needs to be moved in the capillary interchange technique; however, as a practical matter, capillary interchange techniques are generally limited to oil recovery from heavy oil deposits within a few hundred feet of the surface.
It has been estimated that the total oil resources of the United States originally in the ground was about 450 billion barrels of which 120 have already been recovered through conventional primary and secondary techniques. Of the remaining 330 billion barrels, it is believed that 30 can still be recovered by such conventional techniques leaving 300 billion barrels still within the ground. Using oil mining techniques, it is further estimated that two-thirds of this remaining oil or 200 billion barrels could be produced which is more than all the oil that has been recovered in the United States since the first well was drilled in 1859 by Colonel Drake.
Of the three oil mining methods, gravity drainage is the simplest and potentially most effective process for recovering petroleum from conventionally depleted fields. Although general gravity drainage techniques have been used for thousands of years, little if any significant advances have been made in such fundamental areas as mine configuration (e.g., tunnel or drift layout and design) and logging techniques specially adapted to meet the needs and requirements of oil mining by gravity drainage. Rather, the trend has been to try to use conventional mining configurations and logging techniques yet such teachings are often unsuited or at cross-purposes to oil mining. For example, literally all logging techniques use a flexible cable to lower and raise a logging tool within the well hole and such techniques are for the most part totally unsuited for use in upwardly extending holes. As another example, conventional mining configurations generally have as their primary purpose to remove as much of the ore or rock as possible while leaving as little in place for support as is practical. In contrast, a mining configuration for oil recovery by gravity drainage would preferably remove as little rock as possible with the minimum amount of linear tunnel feet for developmental speed and efficiency while creating as much drilling surface area and room as possible for upward drilling, completion, and oil production facilities.
It was with the above in mind that the mine configuration of the present invention was developed. With it, oil production from conventionally depleted fields by gravity drainage can be implemented effectively and efficiently.